This invention relates to a filler unit for automatically topping up a container with liquid, and in particular to a battery filler unit for automatically topping up battery cells with electrolyte in the form of purified water to compensate for losses due to electrolysis and evaporation.
One such battery filler unit consists of a vessel which may be positioned immediately above a battery cell and supplied with water in a manner which maintains a constant head in the vessel. An orifice in the bottom of the vessel communicates with a downpipe which extends downwards from the orifice into the top portion of the cell. Water flows from the vessel to the cell under gravity along a flow path defined by the orifice and the downpipe thereby adding to the electrolyte and causing the level of the electrolyte to rise progressively until the lower end of the downpipe becomes submerged below the level of the electrolyte.
The orifice forms a continuous air seal by action of surface tension in the water being dispensed. As the lower end of the downpipe becomes submerged, air in the downpipe becomes trapped, and a condition is set up for pressure equilibrium in the flow path causing flow from the vessel to the cell to cease.
In one improvement of a battery filler unit a baffle plate is introduced and spaced close to the bottom of the vessel to form a capillary passage which operates in tandem with the orifice to improve the quality of the seal at the head of the downpipe. This improvement forms the subject of U.S. Pat. No. 4,544,044. Resistance to the flow of water under the baffle plate is known to be dependent on the physical dimensions underneath the baffle plate. Problems can sometimes arise when these surface characteristics undergo variations sufficient to interfere with the correct flow of the replenishment water. One method which has been used to help alleviate the problem has been to vary the clearance between adjacent faces formed by the bottom of the vessel and the lower surface of the baffle plate appropriately so as to preserve the requisite flow rate.
An obvious disadvantage of this measure is that the capillarity diminishes with increased spacing, leading to a corresponding sacrifice in the efficacy of the airseal with an increase in through flow and uneven filling of the cells of a multi-celled battery.
According to the invention there is provided a filler unit for use in dispensing a liquid into a container to top up the container to a predetermined desired level, the container being divided by level sensing means into a first pressurizable chamber and a second vented chamber, and the filler unit including a vessel for containing the liquid to be dispensed, means for establishing a predetermined substantially constant head of liquid in the vessel, an outlet orifice defined in the wall of the vessel, a baffle in the vessel spaced sufficiently close to the wall to define a capillary passage between the wall and the baffle, wherein the outlet orifice communicates directly with the pressurizable chamber, with at least that surface of the baffle which defines the capillary passage being hydrophilic, the unit being intended for iocation relative to the container, such that in use the liquid is able to flow from the vessel to the container under gravity along a flowpath having a hydrophilic portion defined by the capillary passage and the orifice into the pressurizable chamber until such time as the liquid level in the container has risen to the desired level within the lower end of the pressurizable chamber to trap air therein, thereby to create a pressure equilibrium in the flowpath which causes the flow from the vessel to the container to cease automatically.
In a preferred form of the invention, the level sensing means comprises a downpipe which terminates short of the base of the container and defines the first pressurizable chamber and divides the container into the first and second chambers, and the orifice is formed in a base wall of the vessel, with the downpipe extending downwardly from the orifice.
Advantageously, at least the capillary passage-defining surface of the baffle plate is hydrophilic by virtue of it being subjected to a surface treatment which serves to increase the wettability thereof.
By the term xe2x80x9chydrophilicxe2x80x9d is meant that the capillary passage is capable of establishing the flowpath within a period of time not exceeding 15 seconds, wherein the capillary passage is substantially dry prior to the establishment of the flowpath.
Typically, the various components making up the filler unit, and in particular the baffle plate and the vessel, are injection moulded from a plastics material, such as polypropylene, with the resultant surface of the components having a gloss finish which is inherently hydrophobic, the baffle plate being hydrophilic by virtue of it being subjected to a surface treatment which serves to increase the wettability thereof.
The surface treatment may include the step of coating at least the operatively lower surface of the baffle plate with a hydrophilic substance, with the coating being sufficiently insoluble to withstand at least initial contact with condensate from the container, which in the case of a lead-acid battery, includes dilute sulphuric acid.
The hydrophilic substance typically includes group II metal salts, which are preferably a calcium and/or a magnesium salt such as calcium magnesium carbonate, and which are functionally insoluble in dilute sulphuric or battery acid.
More typically, the salts are chosen from the group comprising calcium carbonate, calcium hydroxide and calcium magnesium carbonate, or dolomite (CaMg(CO3)2).
Other possible hydrophilic substances or wetting agents include calcium chloride, calcium hypochlorite, and magnesium hydroxide, although the wetting effect in respect of these agents is in most cases reduced as they are functionally neutralized in respect of wetting effect in diluted sulphuric or battery acid.
In an alternative form of the invention, the plastics material from which the baffle plate is injection moulded is pre-mixed with a predetermined quantity of a granular filler which may be a finely divided suspended filler which is exposed on the operatively lower surface of the baffle plate.
Conveniently, the injection moulded baffle plate is subsequently treated with an acid so as to dissolve the exposed filler on the operatively lower surface of the plate, thereby defining pockets which provide a wettable surface. This surface may then be treated with a suitable surfactant such as a detergent or sodium bisulphate to encourage the wetting process.
The filler is preferably a group II metal salt. More preferably, the group II metal salt is soluble in hydrochloric acid, and may be in the form of calcium magnesium carbonate.
The surface treatment may also be achieved by surface oxidization of the injection moulded plastics components.
Physical surface-altering treatments such as flame or corona treatment may also be used.